Suspicious powder mailed to several locations in the US states of New York and New Jersey appeared not to be dangerous, the FBI confirmed on Friday.

The substance was mailed to at least five hotels, including luxury hotels near the site of Sunday’s NFL Super Bowl.

White powder was also sent to the New York business of the former NYC Mayor Rudolph Giuliani. Police said preliminary test showed this powder also posed no threat.

An unnamed federal law enforcement official said the powder from one envelope tested positive for baking soda.

It remains unclear where the letters were sent from.

A number of people who came into contact with the letters were taken to Hackensack University Medical Centre for tests but there were no reported illnesses or injuries, according to a hospital spokeswoman.

Five New Jersey hotels: The Econo Lodge in Carlstadt, a Homestead Suites hotel in East Rutherford, and a Renaissance Inn in Rutherford, all received the letters, according to Carlstadt Police Detective John Cleary.

Homewood Suites General Manager, Thomas Martucci, said the letter he received, which he called “nonsense”, contained yellow powder and a typed letter inside referencing al-Qaida and the Dallas FBI.

Lauren Wallace, a jet company employee from Los Angeles staying at the Homewood Suites, said she saw hazardous-material trucks outside and was shooed back from the lobby to her room around 11:15 am by a hotel employee.

She said she was allowed out of her room about 40 minutes later.

Police were called to Giuliani's firm near Rockefeller Center after a worker opened the suspicious letter addressed to Giuliani around 10:30 am on Friday, police said.